This invention relates generally to the conversion of oxygenates to olefins and, more particularly, to light olefins.
Light olefins serve as feed materials for the production of numerous chemicals. Light olefins have traditionally been produced through the processes of steam or catalytic cracking. The limited availability and high cost of petroleum sources, however, has resulted in a significant increase in the cost of producing light olefins from such petroleum sources.
The search for alternative materials for light olefin production has led to the use of oxygenates such as alcohols and, more particularly, to the use of methanol, ethanol, and higher alcohols or their derivatives. Molecular sieves such as microporous crystalline zeolite and non-zeolitic catalysts, particularly silicoaluminophosphates (SAPO), are known to promote the conversion of oxygenates to hydrocarbon mixtures, particularly hydrocarbon mixtures composed largely of light olefins.
The amounts of light olefins resulting from such processing can be further increased by reacting, i.e., cracking, heavier hydrocarbon products, particularly heavier olefins such as C4 and C5 olefins, to light olefins. For example, commonly assigned, U.S. Pat. No. 5,914,433 to Marker, the entire disclosure of which is incorporated herein by reference, discloses a process for the production of light olefins comprising olefins having from 2 to 4 carbon atoms per molecule from an oxygenate feedstock. The process comprises passing the oxygenate feedstock to an oxygenate conversion zone containing a metal aluminophosphate catalyst to produce a light olefin stream. A propylene and/or mixed butylene stream is fractionated from said light olefin stream and cracked to enhance the yield of ethylene and propylene products. This combination of light olefin product and propylene and butylene cracking in a riser cracking zone or a separate cracking zone provides flexibility to the process which overcomes the equilibrium limitations of the aluminophosphate catalyst. In addition, the invention provides the advantage of extended catalyst life and greater catalyst stability in the oxygenate conversion zone.
Mechanical devices are used for driving fluids to appropriate locations at desired pressures. A pump is a mechanical device or machine that is used to force a liquid phase material from one pressure to a higher pressure. The mechanical work performed by a pump is proportional to the volume of the liquid being pumped times the differential pressure which is outlet pressure minus inlet pressure. Some of the mechanical work is expended in transferring the liquid from one location to another. Pumps are not typically sufficiently powerful to change the volume of the liquid being pumped. A compressor is a mechanical device or machine that is used to force a vapor phase material from one pressure to a higher pressure. The mechanical work performed by a compressor is proportional to the volume of the vapor being pumped times the differential pressure. Compressors typically decrease the volume of the vapor being pumped. Material in the liquid phase is always much more dense than material in the vapor phase. For the same mass of material, the work required to pump liquid is always much less than the work required to pump vapor via compressor.
Further improvements such as relating to reducing or minimizing system processing costs and complexity, however, are desired and are being sought.
In view thereof, there is a need and a demand for improved processing and systems for the conversion of oxygenates to olefins and, more particularly, for such processing and systems such as to result in an increase in the relative amount of light olefins.